[plank]

But there is a reasoning (see my reply above): winning is not possible (only the queen is strong enough against two bishops), so draw should be the goal. And underpromoting to knight is only way to keep the piece for another move while still promoting.

[benmmurphy]

its actually surprising how many difficult puzzles can be solved by a very small look ahead and playing the only move that doesn't lose. i've even seen strong GM solve puzzles like this. this is especially useful when the first move in the puzzle is very clear but there might be 5 or 6 reasonable candidate moves in reply and its just a waste of time to compute each variation.